a(1)=1:1。
a(2)=6:012、021、102、120、201、210。
a(3)=50:00023,00032,00113,00131,00203,00230,00302,00311,00320,01013,01031,01103,01130,01301,01310,02003,02030,02300,03002,03011,03020,03101,03110,03200,10013,10031,10103,10130,10301,10310,11003,11030,11300,13001,13010,13100,20003,20030,20300,23000,3002,30011,30020,30101,30110,30200,31001,31001 10、, 31100, 32000.